Methods for making polyglycerol

Abstract

Methods are provided for making polyglycerol. The methods include heating glycerol at reduced pressure in the absence of a glyceride and in the presence of a catalytic amount of an acid selected from the group consisting of sulfuric acid, triflic acid, hydrochloric acid, hexafluorophosphoric acid, tetrafluoroboric acid and mixtures thereof.

What is claimed is:  
     
       1. A method of making polyglycerol comprising:
 heating glycerol at a temperature of about 120° C. to about 160° C. at a pressure below about 400 mmHg in the absence of a glyceride and in the presence of a catalytic amount of an acid selected from the group consisting of sulfuric acid, triflic acid, hydrochloric acid, hexafluorophosphoric acid, and tetrafluoroboric acid, or mixtures thereof, and removing water during the heating step; 
 wherein the polyglycerol has an  M   w  of at least 50,000 g/mol. 
 
     
     
       2. The method of  claim 1 , wherein the acid is sulfuric acid. 
     
     
       3. The method of  claim 1 , wherein the glycerol is heated at a temperature of about 130° C. to about 150° C. 
     
     
       4. The method of  claim 1 , wherein the glycerol is heated at a temperature of about 140° C. 
     
     
       5. The method of  claim 1 , wherein the glycerol is heated at a pressure at or below about 200 mmHg. 
     
     
       6. The method of  claim 1 , wherein the catalytic amount of acid is about 1 wt % to about 5 wt %. 
     
     
       7. The method of  claim 1 , wherein the heating step is performed in the absence of an added epoxide. 
     
     
       8. The method of  claim 1 , wherein the glycerol is heated under an inert atmosphere. 
     
     
       9. The method of  claim 1 , wherein the polyglycerol is not gelled. 
     
     
       10. The method of  claim 1 , wherein less than about 75 mol % of the glycerol hydroxyl groups are converted. 
     
     
       11. The method of  claim 1 , wherein about 70 mol % to about 75 mol % of the glycerol hydroxyl groups are converted. 
     
     
       12. The method of  claim 1 , wherein the critical extent of reaction, p c , is less than or equal to about 80 mol %. 
     
     
       13. The method of  claim 1 , wherein the critical extent of reaction, p c , is about 70 mol % to about 80 mol %. 
     
     
       14. The method of  claim 1 , wherein the polyglycerol has an  M   w  from about 50,000 g/mol to about 120,000 g/mol. 
     
     
       15. The method of  claim 1 , wherein the polyglycerol has an  M   n  of at least 1,500 g/mol. 
     
     
       16. The method of  claim 1 , wherein the polyglycerol has an  M   n  from about 1,500 g/mol to about 4,000 g/mol. 
     
     
       17. The method of  claim 1 , further comprising:
 monitoring the amount of water produced during the heating step; and 
 discontinuing heating prior to reaching the critical extent of the reaction. 
 
     
     
       18. The method of  claim 1 , further comprising monitoring the conversion of glycerol to polyglycerol. 
     
     
       19. The method of  claim 1 , further comprising purifying the polyglycerol. 
     
     
       20. The method of  claim 1 , further comprising:
 diluting the polyglycerol with water; and 
 contacting the diluted polyglycerol with an ion exchange resin. 
 
     
     
       21. A method of making polyglycerol comprising:
 heating a mixture consisting essentially of glycerol and a catalytic amount of an acid selected from the group consisting of sulfuric acid, triflic acid, hydrochloric acid, hexafluorophosphoric acid, and tetrafluoroboric acid, or mixtures thereof, at a temperature of about 120° C. to about 160° C. and a pressure below about 400 mmHg, and removing water during the heating step; 
 wherein the polyglycerol has an  M   w  of at least 50,000 g/mol. 
 
     
     
       22. The method of  claim 21 , wherein the acid is sulfuric acid.